1. Technical Field
This invention relates to pulse generators and, in particular, pulse generators having variable output pulse occurrence rates.
2. Description of the Prior Art
Variable frequency pulse generators are known in the art and have been used heretofore in providing pulse signals with variable repetition intervals. Such signals are generally required in signaling and control operations. The pulse generators in the known art have advantageously used a single high frequency precision oscillator for obtaining a reference frequency. This frequency is divided by an integer reduction factor to obtain the desired decrease in the output frequency. However, deriving multiple frequency outputs that are close together form a pulse generator of this type requires a great increase in the reference frequency. For example, 100 pulses per second may be derived from an oscillator operating at 200 pulses per second; and 101 pulses per second may be derived from another oscillator operating at 202 pulses per second. But to derive both 100 and 101 from the same oscillator by integer division, the oscillator must operate at 10,100 pulses per second minimum which is the least common multiple of the outputs. Thus, the reference oscillator must operate at a much higher frequency, and multiple stages of count reduction circuits are required to obtain in sufficient numbers a reasonable selection of the lower frequencies desired. Such an arrangement has been found satisfactory where the required reference frequency oscillator is within the limitations of available technology, and cost and space requirements for multistage count reducing circuitry is not a consideration. However, in those arrangements desiring high output frequencies, low cost and low power consumption such as is available with CMOS logic, it is desirable to have the source frequency not differ appreciably from the desired frequency, yet still provide a broad range of desired output frequencies.